1. Fields of the Invention
The present invention relates to a hot-runner mold gate structure, and more particularly, to an open-chamber hot-runner mold gate structure that has a certain temperature at the tip of the sprue gate so as to avoid the melting Polyethylene Terephthalate (PET) from being in contact with the cold molds.
2. Descriptions of Related Art
The conventional hot-runner mold gate structure known toto applicant comprises a first body with a first path defined axially therein. A second body is detachably connected to the first body and has a second path which communicates with the first path. The second body has a flange which is fixed between the top mold and the bottom mold when a hot-runner mold is connected to a mold set. A sprue gate is located in the second path and engaged with the inner bottom of the second path. The head of the sprue gate protrudes from the second body. A heating unit is mounted to the first and second bodies so as to provide heat to the first and second bodies. A cover is connected to the outside of the heating unit.
Because of dis-continuous injection, the second body has one end thereof adjacent to the inside of the fifth groove of the top mold and the inside of the second cover. The heat generated from the heating unit is transferred to the top mold and the head of the sprue gate via the second body. However, during the heat transferring process, the heat loss happens during the contact between metallic parts, so that the temperature of the area enclosed by the inside of the top mold and the head is less than that of the second body in the heating unit. The temperature of the area is inversely proportional to the distance to the heating unit. Because of the gradually reduced temperature, the PET in the area and located at the inside of the top mold and close to the injection opening is crystalized and solidified to form a white-fog-like layer.
Although the crystalized and solidified white-fog-like layer can be melted again by activating the heating unit so that the following PET can normally be ejected, the crystalized and solidified white-fog-like layer of the PET that is attached one the inside of the mold can only be partially melted. Therefore, the melted material located on outside of the head together with the partially melted crystalized and solidified white-fog-like layer of the PET are ejected by the high pressure. The partially melted crystalized and solidified white-fog-like layer of the PET is ejected into the cavity in the mold set by high pressure, the partially melted crystalized and solidified white-fog-like layer of the PET will flow with the melted PET in the cavity to form uneven and ir-regulated traces “S” on the product “B” as shown in FIG. 1. The product with the traces “S” is deemed as an unqualified product.
The present invention intends to provide am improved open-chamber hot-runner mold gate structure to eliminate the shortcomings mentioned above.